Chapter 460 Polycythemia
Polycythemia exists when the red blood cell (RBC) count, hemoglobin level, and total RBC volume all exceed the upper limits of normal. In postpubertal individuals, an RBC mass > 25% above the mean normal value (based on body surface area), or a hematocrit level > 60 (in males) or > 56 (in females) indicate absolute erythrocytosis. A decrease in plasma volume, such as occurs in acute dehydration and burns, may result in a high hemoglobin value. These situations are more accurately designated as hemoconcentration or relative polycythemia because the RBC mass is not increased and normalization of the plasma volume restores hemoglobin to normal levels. Once the diagnosis of true polycythemia is made, sequential studies should be done to determine the underlying etiology (see 
Fig. 460-1 on the Nelson Textbook of Pediatrics website at www.expertconsult.com).
Primary Polycythemia (Polycythemia Rubra Vera)
Pathogenesis
In vitro cultures do not require added erythropoietin to stimulate growth of erythroid precursors. Diagnostic criteria for polycythemia vera were revised by the WHO in 2008 and are listed in Table 460-1.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
